Peculiarities of dehydroaromatization of CH4–C2H6 and CH4 over Mo/ZSM-5 catalysts

Abstract

The peculiarities of dehydroaromatization (DHA) of a CH4–C2H6 mixture over 1–10% Mo/ZSM-5 catalysts (Si/Al = 17, 30, 45) were studied in comparison with reactions of individual hydrocarbons. For a (90 vol.% CH4 + 10 vol.% Ar) mixture, the methane conversion passes through a maximum and decreases with the time-on-stream, being about 12% after 6 h. Experiments with a mixture (85 vol.% CH4 + 5 vol.% C2H6 + 10 vol.% Ar) demonstrated that the presence of ethane leads to the suppression of the methane conversion practically to zero and to an increase in the benzene formation rate in comparison with the (CH4 + Ar) mixture. Characterization of the spent Mo/ZSM-5 catalysts by DTA and TGA showed that both the condensation degree of the carbonaceous deposits (C/H ratio) and their content are higher in the presence of ethane. For both feed compositions, the maximal benzene formation rate was observed over the catalyst with 2 wt% Mo and Si/Al = 17. It is proposed that the formation of C2 intermediates from methane and their further transformations in DHA compete with the ethane aromatization, presumably on the same Mo active sites.

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Acknowledgements

The authors are grateful to Dr. G. S. Litvak for TG-DTA measurements. Financial support of this work was provided in the frame of INTAS YS Fellowship 03-55-1568 and by Integration project of SB RAS No. 73.